Extreme insulin resistance in patients with diabetes is defined as insulin dose requirement of greater than 200 units daily. Currently, U-500 regular insulin is frequently used to treat these patients, however, the slow absorption and prolonged duration of action associated with this formulation does not lend itself to effective closed loop insulin pump therapy. A more rapidly absorbed formulation of concentrated insulin would be desirable in this scenario and would provide the additional benefit of taking up less volume than current insulin preparations. Biodel has studied formulations of recombinant human insulin designed for ultra-rapid absorption at meal time. These formulations use EDTA to chelate zinc atoms, destabilizing recombinant human insulin hexamers. Citric acid is also used to mask surface charges on the insulin molecules inhibiting re-aggregation of monomers and directly facilitating absorption. Experiments to date have shown that EDTA/citrate based formulations at concentrations of up to 400 units/ml remain soluble and stable at 5C. In this application, Biodel proposes to optimize multiple pH 7 aqueous formulations of concentrated recombinant human insulin together with excipients which in U-100 formulations have been shown to be ultra-rapid acting, to provide a minimum of 18 month stability under refrigerated conditions. We will ensure that all current US Pharmacopeia (USP) compendia methods are applicable to these formulations and will develop suitable methods if required. We will demonstrate biological activity in a diabetic swine model and will demonstrate that our formulation is compatible with a marketed insulin pump system for at least 14 days.